Why is my PDF so big? (and how to make it smaller)

Three quick checks to find the cause

1. Work out the size per page. Divide the file size by the number of pages. Compress PDF shows both as soon as you open the file. A few typed pages taking several megabytes almost always means there are large pictures inside.
2. Try to select a sentence. If you can't highlight the words, each page is a picture of text, usually from a scanner, a phone or a "print" that turned pages into images.
3. See what made the file. Open the PDF in Edit PDF metadata and look at "Created with (application)" and "PDF producer". A scanner app, a phone or a word processor tells you a lot about what's inside. (You don't have to save anything.)

The usual causes at a glance

Scanned pages

A scan is a picture of each page, and picture size grows quickly with resolution and color. Epson's scanner help says higher resolution settings make larger files, and gives the example of a letter-size page being about 24 MB at 300 dpi but about 1.3 MB at 72 dpi. Adobe adds that an image's bit depth (how much color information each dot holds) also affects file size, so a black-and-white letter scanned in full color takes more space than it needs.

Fix: for a scan you already have, Compress PDF on Recommended usually makes the biggest difference. If you can scan again, 200 dpi is plenty for most documents and 300 dpi suits very small print. Choose grayscale unless color matters, such as for photos or stamps.

Photos from a phone camera

Phone cameras take large, detailed photos, and a photo of a document is often several megabytes on its own. When you turn photos into a PDF, they're usually stored at full size. JPG to PDF, for example, places JPG and PNG images in the PDF exactly as they are, so ten 3 MB photos make a PDF of about 30 MB.

Fix: make the PDF first, then compress it. Recommended keeps the pages clear for reading on screen. Frame each photo so only the paper is in view: the table around it adds size and nothing useful.

Embedded fonts

Adobe explains that PDFs can be large because fonts are embedded in the file, and that adding a single font can sometimes increase the size a lot. Embedding means the font travels inside the PDF, so the document looks the same on every device. Microsoft says the same about Word documents: embedded fonts increase file size.

Fix: go back to the document you made the PDF from. In Word, Microsoft suggests turning off Embed fonts in the file under File > Options > Save, or, if you need it, choosing Embed only the characters used in the document. Then save as PDF again. Using common fonts instead of decorative ones also helps.

Merged files

When you join PDFs, each file brings its own pictures and fonts. Ten scanned statements merged into one file are about as big as the ten files together. Repeated cover pages, logos and blank pages all add up.

Fix: remove pages you don't need with Delete PDF pages, or do it in the PDF ProMaster Workspace while you merge. Then compress the result.

Files saved many times

Some PDF apps save changes by adding them to the end of the file instead of rewriting it. The earlier versions stay inside, which is why a file you've edited many times can be much larger than a fresh copy. A PDF Association talk on these "incremental saves" notes they can grow significantly over time. Adobe's advice is to use Save As rather than Save, because writing a new file takes less space than adding changes to the old one.

Fix: use Save As in your PDF app, or open the file in Compress PDF and choose Light. Light saves a fresh copy without redrawing anything, so the text stays selectable. If it can't make the file noticeably smaller, the tool tells you instead of giving you a file that's no better.

Word documents can carry extra picture data too. Microsoft suggests choosing Discard editing data under File > Options > Advanced, and using Compress Pictures (on the Picture Format tab) with Delete cropped areas of pictures ticked. Do this before you save as PDF.

Pages "printed" as pictures

If a PDF was made by printing or exporting pages as images, every page is a picture even though it started as typed text. The clue is the same as for a scan: you can't select the words. Where you can, make the PDF again with your app's own Save as PDF or Export option, which normally keeps the text as text. Our guide on how to make a PDF from Word, photos, a web page or a scan shows the built-in options on each device.

Attachments, layers and other extras

A PDF can carry other files inside it as attachments, and some PDFs have layers that can be shown or hidden. If a PDF is large but its pages look plain, this may be why.

Fix: the Recommended and Smallest file levels in Compress PDF build a new PDF from images of the pages as you see them, so attached files and hidden content aren't carried over. Make sure you don't need the attachments first.

Which Compress PDF level to choose

• Light: for typed documents. Text stays selectable. Removes waste inside the file.
• Recommended: for scans and photos. Pages are saved as good-quality images, so the text can't be selected afterwards.
• Smallest file: when size matters more than sharpness.
• Exact size: when a form or email has a limit. It keeps the sharpest version that fits. See how to compress a PDF to a specific size.

Compression happens in your browser, so the file stays on your device. Keep your original, especially if you need to search or copy its text later.

When smaller isn't enough

If the file has to stay sharp, or it's simply long, split it with Split PDF and send it in parts. Trying to email it? Our guide to sending a PDF that's too big to email covers the attachment limits for Gmail, Outlook.com and Yahoo Mail.

Questions

Sources

• Adobe: Why is my PDF so big? (checked 27 October 2026)
• Microsoft Support: Reduce the file size of your Word documents (checked 27 October 2026)
• Epson: How do I decide which resolution to select when scanning? (checked 27 October 2026)
• PDF Association: In defense of the incremental save (2025) (checked 27 October 2026)
• Adobe Help: PDF layers in Acrobat (checked 27 October 2026)